Check Rear Gate Latch Switch
WARNING: This page is about a different car, the 2021 Subaru Ascent. However, it is still accessible from the selected car via links, so may be relevant.
For inspection, refer to "Rear Gate Latch and Actuator Assembly" in "SECURITY AND LOCKS" information. Ref. to SECURITY AND LOCKS>Rear Gate Latch and Actuator Assembly>INSPECTION>ACTUATOR .